The present invention relates generally to the field of lighting and displays, and more particularly to an organic light emitting device capable of white light emissions and a method for producing white light emissions.
Electroluminescent (“EL”) devices, which may be classified as either organic or inorganic, are well known in the graphic display and imaging art. EL devices have been produced in different shapes for many applications. Inorganic EL devices need to be carefully fabricated on crystalline or polycrystalline substrates and thus may prove to be more expensive. On the other hand, organic light emitting devices (“OLEDs”), which have been developed more recently, offer the benefits of low activation voltage and high brightness in addition to simple manufacture, and thus the promise of more widespread application.
An OLED is typically a thin film structure formed on a substrate such as glass or transparent plastic. A light-emitting layer of an organic EL material and optional adjacent organic semiconductor layers are sandwiched between a cathode and an anode. The organic semiconductor layers may be either hole (positive charge)-injection or electron (negative charge)-injection layers and also comprise organic materials. The material for the light-emitting layer may be selected from many organic EL materials that emit light having different wavelengths. The light emitting organic layer may itself comprise multiple sublayers, each comprising a different organic EL material.
To obtain illumination-quality lighting based on organic electroluminescence, a number of solutions have been explored and proposed. For example, one solution utilizes closely arranged OLEDs emitting blue, green, and red light. These colors are mixed to produce white light. In a similar approach, people have achieved white light emissions by incorporating one or more different color fluorescent or phosphorescent dyes into a single OLED. Another approach involves the use of a blue OLED and down-conversion materials to convert some of the blue light into other colors.
However, none of the existing techniques are particularly effective in producing efficient, high accuracy white light. In addition, the use of multiple emissive species gives rise to differential aging of the components of the device with a consequent color change over time as the device ages.
These and other drawbacks exist in known systems and techniques.